There are a large number of optical devices that have two or more ports which receive and transmit light signals. Optical filters, amplifiers, and multiplexers are but a few examples of such devices. Equipment and protocols for efficiently testing such devices are required both in research and manufacturing.
To simplify the following discussion, consider the case of a two-port device such as an optical amplifier. To characterize the device, a signal is applied to a first port and the output from the second port together with the signal reflected back from the first port are analyzed. In addition, the power of the input signal is also monitored. After the first port has been characterized, the roles of the two ports are reversed.
In prior art systems, the ports are reversed by disconnecting and reconnecting the device under test to the measurement equipment. Connections in optical lines are much more problematic than those in electrical circuitry. If the connecting optical line has a fusion connection, the lines must be cut and then refused. This is a time consuming process which is to be avoided if possible. Alternatively, mechanical couplers can be used to make the connections. Unfortunately, the reliability of such coupling devices is poor, and hence, one cannot be sure that the characterization of the device under test is not altered by the properties of the mechanical connection.
These difficulties are even more pronounced in the testing of optical devices having more than two ports. Since each port must be tested as an input port as well as an output port, the number of reconnections required to test a device grows rapidly with the number of ports.
Broadly, it is the object of the present invention to provide an improved apparatus and method for characterizing optical devices.
It is a further object of the present invention to provide an apparatus that does not require reconnection of the test equipment during the characterization of the device.
It is a still further object of the present invention to provide a device that can be utilized in testing optical devices having more than two ports.
These and other objects of the present invention will become apparent to those skilled in the art from the following detailed description of the invention and the accompanying drawings.